Image scanner having system extending function and image correcting function

ABSTRACT

In an image scanner having a flat bed type structure and an automatic document feeding type structure, the scanner includes: an image read unit at least including a lamp, a mirror and CCD sensors to read a manuscript which is put on the structure; an image control unit operatively connected to the image read unit to process an image read by the image read unit; a host computer operatively connected to the image control means; and the image control unit including a main printed-circuit board provided for the original functions of the image scanner, a main connector connecting the image control means to the host computer, a user printed-circuit board selectively provided by a user as an extended slot and the board being mounted within the image control unit, and a user connector connecting the main printed-circuit board to the user printed-circuit board. Further, the image scanner has a function of correction for a difference in an image output between the FB type and the ADF type by adjusting a change rate from the white/black reference level, the gain of the amplifier, the lamp current, or a predetermined conversion formula.

This is a division of application Ser. No. 08/447,808, filed May 23,1995.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an image scanner and, moreparticularly, it relates to an image scanner having a system extendingfunction and an image correcting method between two types of the imagescanner, i.e., a flat bed type and an automatic document feeding type.

2. Description of the Related Art

Recently, image scanners have become widely utilized in various fields,for example, communication, business, designs, education, arts, etc.Accordingly, various functions are required in a recent image scanner inorder to satisfy a user's request. One of functions is an extended slotwhich can be easily realized by the user.

On the other hand, in general, the image scanner is available in twotypical types in accordance with the structural difference, i.e., theflat bed (FB) type and the automatic document feeding (ADF) type. Themain difference between the FB type and the ADF type lies in that amanuscript is not moved in the former, and the manuscript is moved inthe latter when it is read by an image read means. In another aspect ofthe present invention, the difference of an image output between the FBtype and the ADF type can be eliminated.

SUMMARY OF THE INVENTION

The first object of the present invention is to provide an image scannerhaving a function of an extended slot which can be easily mounted by auser within the image scanner.

The second object of the present invention is to provide a correctionmethod in an image scanner having a correcting function for a differencebetween an image output from a flat bed type image scanner or from anautomatic document feeding type image scanner.

In accordance with a first aspect of the present invention, there isprovided an image scanner preferably having a flat bed type structureand an automatic document feeding type structure, including: an imageread unit at least including a lamps a mirror and CCD sensors to read amunuscript which is put on said structure; an image control unitoperatively connected to the image read unit to process an image read bythe image read unit; a host computer operatively connected to the imagecontrol unit; and the image control unit including a mainprinted-circuit board, provided for the original functions of the imagescanner, a main connector connecting the image control unit to the hostcomputer, a user printed-circuit board selectively provided by a user asan extended slot and the board being mounted within the image controlunit, and a user connector connecting the main printed-circuit board tothe user printed-circuit board.

In a preferred embodiment, the image control unit further includes: acontrol circuit operatively connected to said CCD sensors; amicroprocessor connected to the control circuit; a driver and adriver/receiver both connected to the control circuit; a video connectorconnected to the driver to send image signals to the host computer; acontrol connector connected to the driver/receiver to send and receivecontrol signals to/from the host computer; and an extended connectorconnected between the control circuit and the extended slot to send andreceive the image/control signals to/from the extended slot withoutpassing through the driver and driver/receiver.

In another preferred embodiment, the extended connector is set to validstate when the extended slot is connected thereto.

In still another preferred embodiment, the extended connector is usedfor testing the difference between an image output from the flat bedtype and from the automatic document type.

In still another preferred embodiment, the image control unit furtherincludes a selection circuit operatively connected between the controlcircuit and the extended connector for selecting connection to eitherthe driver/receiver or said extended slot.

In accordance with a second aspect of the present invention, there isprovided a correction method in an image scanner having a flat bed typestructure and an automatic document feeding type structure, comprising:a white reference portion provided on a glass plate which holds amanuscript; a black reference portion provided adjacent to the whitereference portion; a lamp unit for irradiating light onto themanuscript; a mirror for reflecting the light irradiated from the lampto said manuscript; CCD sensors for converting images on the manuscriptto electric signals; the lamp unit, the mirror and the CCD sensorsforming an image read unit used commonly in the FB type and the ADFtype; an AGC amplifier connected to the CCD sensors for amplifing anoutput of the CCD sensors and controlling the gain thereof; amicroprocessor; a D/A converter for adjusting the gain of the AGCamplifier in accordance with control by the microprocessor; asample-hold means for sampling an output from the AGC amplifier;

a white level memory for storing a white reference level which isobtained by reading the white reference portion; a white level D/Aconverter for converting an analog white reference level signal, whichis read from the white level memory, to a digital signal; a black levelmemory for storing a black reference level which is obtained by readingthe black reference portion; a black level D/A converter for convertingthe analog black reference level signal, which is read from the blacklevel memory, to the digital signal; an A/D converter having an inputterminal for receiving the analog signal from the sample-hold means, awhite reference terminal for receiving the output from the D/Aconverter, and a black reference terminal for receiving the output fromthe D/A converter, and outputting the digital signal; a work RAM forstoring various working data; and an E² PROM for storing resultant data;

wherein correction of the difference of an image output between the FBtype and the ADF type is performed in such a manner that; first, theimage read unit of the FB type reads a reference manuscript havinguniform reflectance ratio, and a first output of the A/D converter isstored in the work RAM; next, the image read unit of the ADF type readsthe same reference manuscript and outputs a second output from the A/Dconverter, further, a level of the white reference level signal at thewhite reference terminal of the A/D converter is adjusted by controllingthe D/A converter for the AGC which is controlled by the microprocessorso that the second output becomes equal to the first output, and achange rate of the white reference level signal is stored in the E² PROMwhen the first output is equal to the second output; and finally, whenthe image read unit reads the manuscript by using the ADF type, theoutput from the white level D/A converter is changed in accordance withthe change rate which is stored in said E² PROM.

In a preferred embodiment, the correction of the difference of the imageoutput between the FB type and the ADF type is performed in such amanner that; first, the image read unit of the FB type reads thereference manuscript having a uniform reflectance ratio, and the firstoutput of the A/D converter is stored in said work RAM; next, the imageread unit of the ADF type reads the same reference manuscript andoutputs the second output from the A/D converter, further, the gain ofthe amplifier and sample-hold means is adjusted by controlling the D/Aconverter used for the AGC which is controlled by the microprocessor sothat the second output becomes equal to the first output, and the changerate of the gain is stored in the E² PROM when the first output is equalto the second output; and finally, when the image read unit reads themanuscript by using the ADF type, the gain of the amplifier andsample-hold means is changed in accordance with the change rate which isstored in the E² PROM.

In another preferred embodiment, the correction of the difference of theimage output between the FB type and the ADF type is performed in such amanner that; first, the image read unit of the FB type reads thereference manuscript having a uniform reflectance ratio, and the firstoutput of the A/D converter is stored in the work RAM; next, the imageread unit of the ADF type reads the same reference manuscript andoutputs the second output from the A/D converter, further, the tubecurrent of the lamp is adjusted by controlling a D/A converter for tubecurrent which is controlled by the microprocessor so that the secondoutput becomes equal to the first output, and the change rate of thetube current is stored in the E² PROM when the first output is equal tothe second output; and finally, when the image read unit reads themanuscript by using the ADF type, the tube current of the lamp ischanged in accordance with the change rate which is stored in said E²PROM.

In still another preferred embodiment, the correction of the differenceof the image output between the FB type and the ADF type is performed insuch a manner that; first, the image read unit of the FB type reads thereference manuscript having a uniform reflectance ratio, and the firstoutput of the A/D converter is stored in the work RAM; next, the imageread unit of the ADF type reads the same reference manuscript andoutputs the second output from said A/D converter, further, inaccordance with the first and second outputs, a conversion formula isgenerated so that the first output becomes equal to the second output,and the resultant formula is stored in the E² PROM; and finally, whenthe image read unit reads the manuscript by using the ADF type, theoutput of the A/D converter is changed in accordance with the resultantformula which is stored in said E² PROM by using the microprocessor.

BRIEF EXPLANATION OF THE DRAWINGS

In the drawings:

FIG. 1 is a basic structure of an image scanner including an image readunit and an image control unit which is connected to the image readunit;

FIG. 2 is a detailed block diagram of the image scanner;

FIG. 3 is a perspective view of the image scanner;

FIG. 4 is a detailed block diagram of a control unit shown in FIG. 3;

FIG. 5 shows some examples of a video interface for image signals;

FIG. 6 shows some examples of a control interface for control signals;

FIG. 7 shows an interface between a control circuit and an extendedslot;

FIG. 8 is an explanatory view for explaining a main scanning directionand a sub-scanning direction;

FIGS. 9A to 9E are timing charts of the video interface;

FIG. 10 is a detailed circuit of a receiver of FIG. 5;

FIG. 11A and 11B are explanatory views for explaining connection to anexternal unit.

FIG. 12 is a detailed block diagram of the control unit as anotherexample;

FIG. 13A is a detailed block diagram of the control circuit shown inFIG. 4;

FIG. 13B is a detailed block diagram of the control circuit shown inFIG. 12;

FIG. 14 is a basic block diagram of an image scanner using the presentinvention;

FIGS. 15A to 15F are explanatory views for explaining normal readsequence from the manuscript in use of an AGC amplifier;

FIG. 16A shows a basic structure of the image read unit of a FB type;

FIG. 16B shows a basic structure of the image read unit of an ADF type;

FIG. 16C is an explanatory view of the difference of an image outputbetween the FB type and the ADF type;

FIG. 17A is a waveform of the image output in the read operation by theFB type;

FIG. 17B is a read line on a reference paper of FIG. 17A;

FIG. 18 is a detailed circuit diagram of the A/D converter 16 of FIG.14;

FIG. 19 is an explanatory view for explaining correction by means of awhite reference level between the FB type and the ADF type;

FIG. 20 is an explanatory view for explaining correction of a CCD outputbetween the FB type and the ADF type; and

FIGS. 21A and 21B are flowcharts for explaining adjustment processesaccording to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a basic structure of an image scanner including an image readunit and an image control unit which is connected to the image readunit. The image read unit 1 includes CCD image sensors to read amanuscript. The image control unit 2 includes: at least one mainprinted-circuit board 20 having various functions which are essentiallyprovided to operate the image scanner; a main connector 21 to connectthe main printed-circuit board 20 to an external stage (i.e., hostcomputer); and a user connector 22 to connect the main printed-circuitboard 20 to a user printed-circuit board 23 which is selectivelyprovided by a user.

Although a detailed operation will be explained with reference to FIG.2, briefly, the image control unit 2 receives a control signal from anexternal stage through a receiver, sends the control signal to theexternal stage through a driver, and sends an image signal to theexternal stage through the driver. Further, the image control unit 2controls the operation of the image read unit 1, and sends the imagesignal to the external stage after predetermined image processingthereto.

The main printed-circuit board 20 has functions to control the operationof the image read unit 1. The main connector 21 outputs the image signaland the control signal to the external stage through the driver which ismounted on the main printed-circuit board 20, and receives the controlsignal from the external stage through the receiver which is mounted onthe main printed-circuit board 20.

The connector 22 is provided for the user printed-circuit board 23 whichis selectively mounted by the user, and directly sends the controlsignal to the user printed-circuit board 23 without passing through thedriver/receiver, and directly sends the image signal to the userprinted-circuit board 23 without passing though the driver.

As one embodiment, when the user printed-circuit board 23 is mounted tothe connector 22, the control signal through the main connector 21becomes invalid and the control signal through the connector 22 becomesvalid. As the other embodiment, both connectors 21 and 22 become valid.

As explained above, in the first aspect of the presently invention, theconnector 22 is provided in the image control unit 2 to mount the userprinted-circuit board 23 therein. The connector 22 directly connects theimage signal to the user printed-circuit board 23 without passingthrough the driver, and directly connects the control signal to the userprinted-circuit board 23 without passing through the drive/receiver.

That is, the feature of the image control unit 2 lies in that the imagesignal in the unit 2 is directly provided to the user without passingthrough the driver and the control signal in the unit 2 is also directlyprovided to the user without passing through the driver/receiver.

Accordingly, when the user wishes to obtain a new image process which isnot provided in the image control unit, the user connects the userprinted-circuit board 23 to the connector 22. In this case, as explainedabove, since the image signal from the connector 22 to the userprinted-circuit board 23 is not passed through the driver, it ispossible for the user to obtain the new image process, which is requiredby the user, without any limitation provided by the driver.

Further, when the user wishes to connect another new system which cannotbe connected by a current external interface of the image control unit,the user provides a new user printed-circuit board which can connect thenew system to the connector 22. As explained above, since the imagesignal and the control signal from the connector 22 to the new userprinted-circuit board 23 are not passed through the driver/receiver, itis possible for the user to obtain the new image process, which isrequired by the user, without any limitation provided by thedriver/receiver.

FIG. 2 is a detailed block diagram of the image scanner, and FIG. 3 is aperspective view of the image scanner. In FIG. 2, the image control unit30 includes a carrier unit 31, an automatic document feeder (ADF) unit32, a flat bed (FB) unit 33, a image control unit 34, an imageprocessing unit 35, an operator panel 36, a power source 37, an extendedslot 38, a junction unit 39, a video connector 40 for the image signal,a control connector 41 for the control signal, and a extended connector42 for the extended slot 38. The connectors 40 and 41 are connected to ahost computer.

The carrier unit 31 corresponds to the image read unit 1 of FIG. 1 andincludes CCD image sensors and a lamp unit for reading an image from amanuscript.

The ADF unit 32 is formed by a glass plate, to hold the manuscript, astacker to store the manuscript after read operation, a feedingmechanism to feed the manuscript one by one, an ADF motor to move thefeeding mechanism, and various sensors to control the operation of thefeeding mechanism and rotation of the ADF motor.

The FB unit 33 is formed by the flat bed to hold the manuscript, acarrier motor to move the carrier unit 31, and position sensors todetect the position of the carrier unit 31.

As shown in FIG. 3, the image scanner used for the present inventionincludes both the ADF type and the FB type. In FIG. 3, reference number50 denotes the flat bed (FB), and reference number 51 denotes amanuscript base used for the ADF type. Further, reference number 52 is astacker for the ADF type. In the ADF type, manuscripts on the base 51are automatically transferred one by one, and each manuscript is read bythe image read unit. In the FB type, the manuscript is manually put onthe glass plate one by one.

Briefly, the control unit 34 controls the operations of the carrier unit31, the ADF unit 32 and FB unit 33 in accordance with instructions froma host computer. Further, the image control unit 34 receives imagesignals read by the carrier unit 31, and performs A/D conversion on thesignals. Still further, the image control unit 34 generates variousvideo interface signals, and sends them to the host computer asexplained in detail below.

The image processing unit 35 performs various processes on the imagesignal, for example, emphasis and smoothing of the image, conversionfrom white image to black image and vice versa, a mirror image generatedfrom the original image, extraction of outline of the image, separationof the image from the manuscript mixed with characters and photos,half-tone dot meshing of the image, and enlargement and reduction of theimage.

The operator panel 36 is operated by the user to input variousinstructions to the image scanner. The power source 37 receives ACvoltages, for example, 100 to 120 (v) and 200 to 240 (v), and generatesDC voltages, for example, +5 (v), +/-15 (v) and +24 (v) to operate theimage control unit 34.

The extended slot 38 is equivalent to the user printed-circuit board 23which is selectively provided by the user when the user wishes to extendthe functions of the image scanner. The junction unit 39 is a connectorto connect between the image control unit 34 and the carrier unit 31,the FB unit 33 and the operator panel 36. The ADF unit 32 is directlyconnected to the image control unit 34 without passing through thejunction unit 39. A

The video connector 40 is provided for connecting between the imagecontrol unit 34 and the host computer, and is used to output the imagesignal to the host computer. The control connector 41 is provided forconnecting between the image control unit 34 and the host computer, andis used to input/output the control signal from/to the host computer.The extended connector 42 is provided for connecting between the imagecontrol unit 34 and the extended slot. The extended slot 38 is connectedto the host computer through the user printer-circuit board.

As explained above, in the first aspect of the present invention, theextended connector 42 is provided for connecting the extended slot 38which connects the user printed-circuit board within the image scanner.

FIG. 4 is a detailed block diagram of the image control unit shown inFIG. 3. As shown in the drawing, the image control unit 34 includes: anamplifier (AMP) 70 for amplifing the output of a CCD image sensor 60; anA/D converter 71 for converting analog signals to digital signals; acontrol circuit 72 for processing output signals from the A/D converter71 and the carrier unit 31; a micro processor (MPU) 73 for supportingthe control circuit 72; a driver 74 for outputting the image signal tothe host computer, and a driver/receiver 75 for inputting/outputting thecontrol signal from/to the host computer.

The control circuit 72 is directly connected to the extended slot 38through the extended connector 42 without passing through the driver 74to send the image signal, and directly connected to the extended slot 38through the extended connector 42 without passing through thedriver/receiver 75 to send the control signal. That is, the controlsignal from the control circuit 72 can take two routes, one is connectedto the control connector 41 through the driver/receiver 75 and the otheris directly connected to the extended connector 42.

A video interface includes various image signals which are output fromthe driver 74 to the host computer through the video connector 40. Acontrol interface (in general, RS-232-C is used) includes variouscontrol signals which are output from the driver/receiver 75 to the hostcomputer through the control connector 41.

FIG. 5 shows some examples of the video interface for image signals,FIG. 6 shows some examples of the control interface for control signals,and FIG. 7 shows the interface between the control circuit 72 and theextended slot 38. In FIG. 5, the signals "FAIL", "VGATE", "HGATE", "VCL"and "V0" to "V7" represent the video interface between the host computerand the image control unit, and the symbol "*" indicates negative logic.The signal FAIL represents an abnormal state of the image scanner, thesignal VGATE represents the validity of video data in the sub-scanningdirection (i.e., the direction which is perpendicular to main scanningdirection of the CCD image sensor 60), the signal HGATE represents thevalidity of the video data at the main scanning direction, the signalsV0 to V7 represent the eight bits of video data, and the signal VCLrepresents the sampling clock of the video data V0 to V7. Further, inthe driver 74, the symbol "D" represents a driver element.

In FIG. 6, the signal "TXD" represents control data to be sent to thehost computer, the signal "RTS" represents a sending request signalwhich requests the control data from the host computer, the signal "DTR"represents a ready state of its own image scanner. These signals aresent to the host computer through the driver element. The symbol "R"represents a receiver element.

In FIG. 7, the interface between the control circuit 72 and the extendedslot 38 includes the control signal (TXD, *RTS, *DTR, RXD, *CTS, and*DSR), the image signal (FAIL, VGATE, HGATE, *VCL, and V0-V7), andothers (+5, 0(V), and CONNECT).

The signal "RXD" represents the control data from the host computer, thesignal "CTS" represents an acknowledge signal for the sending requestsignal RTS from the host computer, the signal "DSR" represents a readystate of the host computer. These signals are sent from the hostcomputer to the image scanner through the receiver elements.

FIG. 8 is an explanatory view for explaining the main scanning directionand the sub-scanning direction, FIGS. 9A to 9E are timing charts of thevideo interface, and FIG. 10 is a detailed circuit of the receiver ofFIG. 5. As explained above, the signal VGATE represents the validity ofvideo data at the sub-scanning direction, and the signal HGATErepresents validity of the video data at the main-scanning direction. Inthe drawing, the symbol "*" indicates negative logic.

In FIGS. 9A to 9E, the eight bits of video data V0 to V7 are output fromthe driver 74 in response to the clock VCL. The video data V0 to V7 areformed as eight pixels data when they are binalized, and formed as onepixel data when they are not binalized.

Through the control interface, the host computer generates variouscontrol signals including initialization of the mechanism, read size anddensity of the manuscript, situation of mechanism, FB or ADF type, etc.,to the image control unit 34.

The control circuit 72 sends the image signal to the extended slot 38through the extended connector 42 without passing through the driver 74,and sends or receives the control signal to/from the extended slot 38through the extended connector 42 without passing through thedriver/receiver 75. As shown by arrows in FIG. 7, the signals TXD, RTSand DTR are sent from the control unit to the host computer, and thesignals RXD, CTS and DSR are sent from the host computer to the controlunit. Further, the signal FAIL is sent from the control unit to the hostcomputer. Still further, signals VGATE, HGATE, *VCL and V0 to V7 aresent or received between the control unit and the host computer.

When the control circuit 72 detects a connection of the extended slot 38to the connector 42 in accordance with the connection signal (CONNECT)from the extended slot, the control circuit 72 sets the control signal,which is not passed through the driver/receiver, to the valid statethrough the connector 22. As another embodiment, both connectors 21 and22 become valid and the control circuit 72 sets the control signal tothe valid state using a predetermined program.

When the image signal passes through the driver 74, a transfer rate perone byte is limited to, for example, 0.8 μs, in a conventional art.Further, when the control signal passes through the driver/receiver 75,a transfer rate per one byte is limited to, for example, 100 μs in theconventional art. However, according to the present invention, since theextended slot 38 is directly connected to the control unit 34 withoutpassing through the driver 74 and driver/receiver 75, it is possible touse the control signal without any limitation.

FIGS. 11A and 11B are explanatory views for explaining the connection tothe external stage. In FIG. 11A, a connector for an external unitincludes the connectors 40, 41 and 42 of FIG. 2. That is, when the userwishes to obtain an image signal processed by a new signal process whichis not included in the image scanner, the extended slot 38 is connectedto the extended connector 42 (see FIG. 2). Further, the image signal ofthe extended slot 38 is returned to the control circuit 72 and output tothe video connector 40 and the control connector 41 through the driver74 and the driver/receiver 75.

In FIG. 11B, the connector for the external unit includes the videoconnector 40 and the control connector 41, and a connector for anexternal network includes the extended connector 42. That is, when theuser wishes to connect an external network which cannot be connected tothe video/control interface of the image scanner 30, the extended slot38 is connected to the extended connector 42 (see FIG. 2).

As explained in FIG. 4, as the image signal from the extended connector42 to the extended slot 38 is not passed through the driver 74, it ispossible to easily perform the image processing which is required by theuser without any limitation by the driver 74. In this case, when a highspeed processing is required by the user, the video interface is used.On the contrary, when the high speed processing is not required by theuser, the control interface is used.

Further, as the control signal from the extended connector 42 to theextended slot 38 is not passed through the driver/receiver 75, it ispossible to easily perform the connection to a network which is requiredby the user without any limitation by the driver/receiver 75.

FIG. 12 is a detailed block diagram of the image control unit 34 asanother example, and FIG. 13B is a detailed block diagram of the controlcircuit 72' shown in FIG. 12. As shown in the drawing, a selectioncircuit 76 is provided for preventing a collision of the controlsignals. The control circuit 72' includes an image control portion and ahost control portion. The image control portion receives the output ofthe A/D converter 71 and outputs the image signal to the driver 74through a tri-state element. The host control portion receives theoutput of the microprocessor 73 and outputs the control signal to thedriver/receiver 75 as explained below.

That is, the control signal is directly connected from the controlcircuit 72' to the driver/receiver 75 as a first route, and is returnedfrom the driver/receiver 75 through the selection circuit 76 as a secondroute. That is, the control circuit 72' receives the control signaleither through the driver/receiver 75 or through the extended connector42. In this case, when the extended slot 38 is not connected to theextended connector 42, the first route is selected. On the other hand,when the extended slot 38 is connected to the extended connector 42, thesecond route is selected. Accordingly, it is possible to preventcollision of the control signals since the control signal can select oneof two routes in accordance with connection of the extended slot 38.

FIG. 13A is a detailed block diagram of the control circuit 72 shown inFIG. 4. The control circuit 72 includes an image control portion and ahost control/extended control portion. The image control portionreceives the output of the A/D converter 71 and outputs the image signalto the driver 74 through the tri-state element. The hostcontrol/extended control portion receives the output of the microprocessor 73 and receives/outputs the control signal from/to thedriver/receiver 75.

As shown in the drawing, the control signal is directly sent/receivedto/from the driver/receiver 75. The connect signals CONNECT are providedfrom the extended connector 42 to the host control/extended controlportion. That is, there are two routes for the control signal, i.e., one(first route) is provided through the driver/receiver 75, and the other(second route) is provided through the extended connector 42 withoutpassing through the driver/receiver 75. When the extended slot 38 isconnected to the extended connector 42, the second route is selected bythe predetermined program.

The following explanations are given to the second aspect of the presentinvention. The second aspect of the present invention relates to thecorrection method for the difference of the image output between the FBtype and the ADF type so as to eliminate the difference for every imagescanner.

FIG. 14 is a basic block diagram of an image scanner using the presentinvention. In FIG. 14, reference number 2 denotes a manuscript to beread, 3 a glass plate, 3a a white reference portion, 3b a blackreference portion, 4 an image read unit, 5 a lamp, 6 a mirror, and 7 aCCD (charge coupled device) image sensor. Reference numbers 8, 8', 9 and9' are explained in FIG. 16B.

Reference 10 denotes a lamp inverter, 11 a D/A converter for controllingtube current to the lamp, 12 an automatic gain control (AGC) amplifier,13 a D/A converter for a gain control of the AGC amplifier, 14 asample-hold circuit, 15 a transistor for controlling the tube current tothe lamp, 16 an A/D converter, 17 a memory for storing white level(below, white level memory), 18 a D/A converter for converting whitelevel (white level D/A converter), 19 a D/A converter for convertingblack level (black level D/A converter), 20 a memory for storing blacklevel (below, black level memory), 21 a microprocessor, 22 a workmemory, and 23 an electrically erasable programmable read only memory(E² PROM).

The manuscript 2 is put on the glass plate 3 in the FB type. The whitereference portion 3a and the black reference portion 3b are providedinside of the glass plate 3. The lamp 5, the mirror 6 and the CCD sensor7 are provided in the image read unit 4 which can move freely leftwardand rightward under the glass plate 3.

The light irradiated from the lamp 5 is reflected by the rear surfacesof the manuscript 2 or the glass plate 3, and the reflected light istransferred to the CCD image sensor 7 through the mirror 6 (see dottedline). The lamp inverter 10 is provided for converting the DC current tothe AC current so that it is possible to obtain the AC current which isset by the microprocessor 21. The setting AC current from the lampinverter 10 is supplied to the lamp 5, and the setting AC current isinformed from the microprocessor 21 through the D/A converter 11 for thelamp current and the transistor 15 for the lamp current.

The output of the CCD image sensor 7 is supplied to the AGC amplifier12. The gain of the AGC amplifier 12 is controlled by the D/A converter13 of which output voltage is adjusted by the microprocessor 21. Theoutput of the AGC amplifier 12 is supplied to an input terminal IN ofthe A/D converter 16 after a sample-hold operation by the sample-holdcircuit 14.

The A/D converter 16 has the input terminal IN, a terminal for whitereference level (below, white reference terminal) REFW, and a terminalfor black reference level (below, black reference terminal) REFB. Theoutput of the white level D/A converter 18 is input to the whitereference terminal REFW, and the output of the black level D/A converter19 is input to the black reference terminal REFB. The white level memory17 can store image data for one line, and the black level memory 20 alsocan store image data for one line. As shown in the drawing, the readdata from the white level memory 17 is input to the white level D/Aconverter 18, and the read data from the black level memory 20 is inputto the black level D/A converter 19.

The microprocessor 21 can control the output of the D/A converter 11 forthe tube current of the lamp, the output of the D/A converter 13 for thegain control of the AGC amplifier 12, the read/write operations for thewhite level memory 17 and the black level memory 20, the output of theA/D converter 16, and the read/write operation for the work RAM and E²PROM through MPU buses.

FIGS. 15A to 15F are explanatory views for explaining a normal readsequence from the manuscript 2 and use of the AGC amplifier. In thedrawing, "IN" corresponds to the terminal IN, "REFW" corresponds to theterminal REFW and "REFB" correspond to the terminal REFB in the A/Dconverter 16. Further, X"FF" corresponds to the white reference leveland X"00" corresponds to the black reference level. Still further, "LW"represents the white level, and "LB" represents the black level.

First, the image read unit 4 is moved to the white reference portion 3ain order to read the white reference level. Next, the gain of the AGCamplifier 12 is adjusted by the following manners. That is first, thewhite level X"FF" (for example, 255) is input from the white levelmemory 17 to the white level D/A converter 18. Next, the black level(for example, 0) is input from the black level memory 20 to the blacklevel D/A converter 19. Further, the gain of the AGC amplifier 12 isadjusted in such a way that the output of the A/D converter 16 becomeslarger than "0" and smaller than "255". After the gain of the AGCamplifier 12 is adjusted based on the above processes, the output of theA/D converter 16 is sequentially written into the white level memory 17through the MPU bus.

After the white reference data are written into the white level memory17, first, the image read unit 4 is moved to the black reference portion3b in order to read the black reference level. Next, the output of theA/D converter 16 is sequentially written into the black level memory 20.After the black reference data is written into the black level memory20, the read data of the white level memory 17 is input to the whitelevel D/A converter 18, and the read data of the black level memory 20is input to the black level D/A converter 19. The read operation for themanuscript is started after the above processes are completed.

In the read operation for the manuscript, when the image signal of thei-th bit of the CCD image sensor 7 is input to the terminal IN of theA/D converter 16, the i-th white reference data of the white levelmemory 17 is input to the white level D/A converter 18, and the i-thblack reference data of the black level memory 20 is input to the blacklevel D/A converter 19.

In the above explanation, although the gain of the AGC amplifier 12 isadjusted so as to match an input range of the A/D converter 16, it ispossible to adjust an amount of the lamp 5 so as to match an input rangeof the A/D converter 16 instead of gain adjustment.

FIGS. 16A to 16C are explanatory views for explaining a difference ofgradation (i.e., a difference of the image output level) between the FBtype and the ADF type image scanner. That is, FIG. 16A shows a basicstructure of the image read unit of the FB type image scanner, and FIG.16B shows a basic structure of the image read unit of the ADF type imagescanner. Further, FIG. 16C is an explanatory view of the difference ofthe image output between the FB type and the ADF type.

In FIGS. 16A and 16B, reference 1 denotes a covering member for themanuscript, 3' a glass plate, 8 a drive roller, 8' a sub-drive roller,and 9 a guide member. The same reference numbers as in previous drawingsare attached to the same components. In the image scanner using thepresent invention, it is possible to read the manuscript using both theFB type and the ADF type by using only one image read unit 4.

In FIG. 16A, in the read operation using the FB type, the manuscript 2is put on the glass plate 3 and the image read unit 4 is moved from theleft to the right.

In FIG. 16B, the sub-rollers 8' are provided to both end of the guidemember 9. In the ADF type, the image read unit 4 is fixedly provided tothe left end of the glass plate 3'. The manuscript 2 is inserted betweenthe drive roller 8 and the sub-drive roller 8'. When the drive roller 8is rotated in the counterclockwise direction, the manuscript istransferred to the left. The light from the lamp 5 is reflected from therear surface of the manuscript 2, and the reflected light is transferredto the CCD image sensor 7 through the mirror 6.

In FIG. 16C, the chain dotted lines show the white reference level. Inthis case, the left solid line shows the output level of the FB type,and the right solid line shows the output level of the ADF type at theA/D converter 16. Further, the ordinate represents the image outputlevel, and the abscissa represents the time (i.e., distance along theCCD image sensor from one end thereof).

As is obvious, there is a difference of gradation "d" (i.e., differenceof output level) between the FB type and the ADF type. This difference"d" is caused by various factors, for example, the amount of the lightreflected from the manuscript, the reflectance ratio of the coveringmember 1 of the FB type, the gap between the manuscript and the glassplate at the ADF type, the influence of peripheral light, etc.

In the image scanner which includes the FB type and ADF type, it isnecessary to eliminate the difference "d" in order to obtain ahigh-quality output image.

In order to eliminate the difference "d" between the FB type and the ADFtype, the following two methods, i.e., mechanical and electricalmethods, are known in a conventional art.

As the mechanical method, (1) in the ADF type, one method is to set thegap between the glass plate 3' and the sub-drive roller 8' as narrow aspossible in order to avoid separating the manuscript 2 and the glassplate 3, and (2) in the ADF type, another method is to provide the morewidth (in the left and right direction) along the glass plate 3' inorder to obtain better contact between the glass plate 3' and themanuscript 2 so that the amount of the peripheral light at the readposition is the same as that in the FB type.

However, the above two methods have the following problems. For item(1), when the gap between the glass plate 3' and the sub-drive roller 8'is reduced, the thickness of a paper which can be used as the manuscript2 is limited in order to ensure smooth movement of the paper. For item(2), when the size of the glass plate becomes large, the cost of theimage scanner increases. Further, since the movement time for the paperbecomes longer, the feeding efficiency of the paper becomes worse.

On the other hand, as the electrical method, one method is to check thedifference "d" of the output level between the ADF type and the FB typeregarding some image scanners, to obtain an average value of thedifference of the gradation, and to determine the correction value (%)of the white reference value of the ADF type. Further, in the readoperation using the ADF type, the above average value is applied to allimage scanners, and the white reference level is changed in accordancewith the average value in order to eliminate the difference of the imageoutput between the FB type and the ADF type.

However, in the above electrical method, since the white referencelevels for all image scanners are uniformly adjusted to thepredetermined correction value, it is difficult to correct a largedifference exceeding the average value.

The second aspect of the present invention aims to eliminate adifference in the image output between the ADF type and the FB typeimage scanner.

As shown in FIG. 14, the image scanner using the second aspect of thepresent invention includes: the lamp 5 for irradiating light onto amanuscript 2; the CCD image sensor (7); the AGC amplifier (12) foramplifying the output of the CCD image sensor and controlling the gainthereof by controlling the output voltage of the D/A converter (13)which is controlled by the microprocessor (21); the white level memory(17) for storing the white reference level which is obtained by readingthe white reference portion (3a); the white level D/A converter (18) forconverting the analog white reference level signal, which is read fromthe white level memory (17), to the digital signal; the black levelmemory (20) for storing the black reference level which is obtained byreading the black reference portion (3b); the black level D/A converter(19) for converting the analog black reference level signal, which isread from the black level memory (20), to the digital signal; and theA/D converter (16) having the input terminal (IN) for receiving theanalog signal from the amplifying/sample-hold units (12, 14, 13), thewhite reference terminal (REFW) for receiving the output from the D/Aconverter (18), and the black reference terminal (REFB) for receivingthe output from the D/A converter (19), and outputting the digitalsignal.

In the above structure, the lamp (5), the mirror (6) and the CCD imagesensor (7) structure the image read unit (4) which is used commonly inthe FB type and the ADF type.

According to a first embodiment of a correction method for correctingthe difference of the image output (i.e., difference of the gradation)between the FB type and the ADF type, the correction method uses thefollowing steps.

First, the image read unit (4) of the FB type reads a referencemanuscript having uniform reflectance ratio, and a first output of theA/D converter (16) is stored in the work RAM (22).

Next, the image read unit (4) of the ADF type reads the same referencemanuscript and outputs a second output from the A/D converter (16).Further, the level of the white reference level signal at the whitereference terminal (REFW) of the A/D converter (16) is adjusted bycontrolling the D/A converter (13) which is controlled by themicroprocessor (21) so that the second output becomes equal to the firstoutput, and a change rate of the white reference level signal is storedin the E PROM (23) when the first output is equal to the second output.

Finally, when the image read unit (4) reads the manuscript by using theADF type, the output from the white level D/A converter (18) is changedin accordance with the change rate which is stored in the E² PROM (23).

According to a second embodiment of the correction method, the secondmethod used the following steps.

First, the image read unit (4) of the FB type reads the referencemanuscript having a uniform reflectance ratio, and the first output ofthe A/D converter (16) is stored in the work RAM (22).

Next, the image read unit (4) of the ADF type reads the same referencemanuscript and outputs the second output from the A/D converter (16).Further, the gain of the amplifier and sample-hold units (12, 14, 13) isadjusted by controlling the D/A converter (13) which is controlled bythe microprocessor (21) so that the second output becomes equal to thefirst output, and the change rate of the gain is stored in the E² PROM(23) when the first output is equal to the second output.

Finally, when the image read unit reads the manuscript by using the ADFtype, the gains of the amplifier and sample-hold units (12, 14, 13) arechanged in accordance with the change rate which is stored in the E²PROM (23).

According to a third embodiment of the correction method, the thirdmethod uses the following steps.

First, the image read unit (4) of the FB type reads the referencemanuscript having a uniform reflectance ratio, and the first output ofthe A/D converter (16) is stored in the work RAM (22).

Next, the image read unit (4) of the ADF type reads the same referencemanuscript and outputs the second output from the A/D converter (16).Further, the tube current of the lamp (5) is adjusted by controlling theD/A converter (11) which is controlled by the microprocessor (21) sothat the second output becomes equal to the first output, and the changerate of the tube current is stored in the E² PROM (23) when the firstoutput is equal to the second output.

Finally, when the image read unit reads the manuscript by using the ADFtype, the tube current of the lamp (5) is changed in accordance with thechange rate which is stored in the E² PROM (23).

According to a fourth embodiment of the correction method, the forthmethod uses the following steps.

First, the image read unit (4) of the FB type reads the referencemanuscript having uniform reflectance ratio, and the first output of theA/D converter (16) is stored in the work RAM (22).

Next, the image read unit (4) of the ADF type reads the same referencemanuscript and outputs the second output from the A/D converter (16).Further, in accordance with the first and second outputs, a conversionformula is generated so that the first output becomes equal to thesecond output, and the resultant formula is stored in the E² PROM (23).

Finally, when the image read unit reads the manuscript by using the ADFtype, the output of the A/D converter is changed in accordance with theresultant formula which is stored in the E² PROM (23) by using themicroprocessor.

In the case of the above first embodiment, for example, it is assumedthat the input level of the white reference signal at the whitereference terminal (REFW) is given to "100", and the input level of theblack reference signal at the black reference terminal (REFB) is givento "0". Under the above condition, it is assumed that the first outputof the A/D converter (16) when the manuscript 2 is read by the FB typeis given to "50", and the second output of the A/D converter (16) whenthe manuscript 2 is real by the ADF type is given to "40".

In this case, since the first output and the second output are differenteach other, the input level of the white reference signal which is inputto the A/D converter (16) by the ADF type is adjusted. That is, if theoutput of the A/D converter (16) becomes "50" when the level of thewhite reference signal is given to "80" in the ADF type, the change rate(i.e., 80/100) is stored in the E² PROM (23). After above steps, theinput level of the white reference signal at the A/D converter (16) inthe normal read operation by the ADF type is adjusted to "80/100" of theinput level of the white reference signal in the normal read operationby the FB type.

In the case of the second embodiment, for example, although the sameconditions as the first embodiment are given, it is assumed that theinput level of the white reference signal at the white referenceterminal (REFW) is given to "100", and the input level of the blackreference signal at the black reference terminal (REFB) is given to "0".Under the above condition, it is assumed that the first output of theA/D converter (16) when the manuscript 2 is read by the FB type is givento "50", and the second output of the A/D converter (16) when themanuscript 2 is read by the ADF type is given "40".

In this case, since the first output and the second output are differenteach other, the gain of the amplifier and sample-hold units is adjustedwhen the manuscript is read by the ADF type. That is, if the output ofthe A/D converter becomes "50" when the gain of the amplifier andsample-hold units at the ADF type is given to "50/40" of the gain of theamplifier and sample-hold units at the FB type, the change rate (i.e.,50/40) is stored in the E² PROM (23). After above steps, the gain of theamplifier and sample-hold units at the normal read operation by the ADFtype is given to "50/40" of the gain of the amplifier and sample-holdunits at the normal read operation by the FB type.

In the case of the third embodiment, for example, although the sameconditions as the second embodiment are given, it is assumed that theinput level of the white reference signal at the white referenceterminal (REFW) is given to "100", and the input level of the blackreference signal at the black reference terminal (REFB) is given to "0".Under the above condition, it is assumed that the first output of theA/D converter (16) when the manuscript 2 is read by the FB type is givento "50", and the second output of the A/D converter (16) when themanuscript 2 is read by the ADF type is given to "40".

In this case, since the first output and the second output are differenteach other, the tube current flowing in the lamp is adjusted. That is,if the output of the A/D converter (16) becomes "50" when the tubecurrent of the lamp at the ADF type is given to "50/40" of the tubecurrent at the FB type, the change rate (i.e., 50/40) is stored in theE² PROM (23). After above steps, in the normal read operation by the ADFtype, the tube current of the lamp is given to "50/40" of the tubecurrent in the normal read operation by the FB type.

In the case of the fourth embodiment, for example, although the sameconditions as the third embodiment are given, it is assumed that theinput level of the white reference signal at the white referenceterminal (REFW) is given to "100", and the input level of the blackreference signal at the black reference terminal (REFB) is given to "0".Under the above condition, it is assumed that the first output of theA/D converter (16) when the manuscript 2 is read by the FB type is givento "50", and the second output of the A/D converter (16) when themanuscript 2 is read by the ADF type is given to "40".

In this case, the conversion formula is generated in order to correctthe output of the A/D converter (16) as follows.

V_(ADF) =an output of the A/D converter×50/40

Where, V_(ADF) is a corrected output.

In the normal read operation by the ADF type, the output of the A/Dconverter is corrected based on the above conversion formula, and theresultant data is used as the image output from the A/D converter.

FIG. 17A is a waveform of the image output in the read operation by theFB type, and FIG. 17B is a read line on a reference paper of FIG. 17A.In FIG. 17A, a chain dotted line denotes the white reference level andthe black reference level, and a solid line denotes the amplified outputof the CCD image sensor (i.e., output from the sample-hold circuit 14,see, FIG. 14). On the black reference level, the first dot representsthe first bit, the center dot represents the i-th bit, and the last dotrepresents the n-bit. Further, the point "A" denotes the level of theamplified output of the CCD image sensor at the i-th bit in the vicinityof the center of the paper. In FIG. 17B, the reference paper has auniform reflectance ratio.

FIG. 18 is a detailed circuit diagram of the A/D converter 16 of FIG.14. Reference numbers (22) denote comparators 1 to 256, and referencenumber 23 denotes a calculation circuit. The upper terminal correspondsto the terminal REFW in the A/D converter and used to input the whitelevel, the center terminal corresponds to the terminal IN in the A/Dconverter and used to input the CCD output through the sample-holdcircuit 14, and the lower terminal corresponds to the terminal REFB inthe A/D converter and used to input the black level. Resistors Rl to Rnare connected in series between the terminal REFW and the terminal REFB.

As shown in the drawing, one input terminal of each comparator 22 isconnected to a common node between adjacent resistors, and the otherterminal of each comparator 22 is connected in common to the terminal INof the CCD output. Accordingly, the levels at the terminals REFW or REFBare applied to one input terminal of each comparator through theresistors, and the amplified output of the CCD image sensor is directlyapplied to the other input terminal of each comparator 22. Further, eachoutput of the comparators 22 is sent to the calculation circuit 23 whichoutputs the digital signals D0 to D7. These outputs correspond to theoutput of the A/D converter 16 of FIG. 14.

The outputs from the A/D converter 16 are determined in accordance withthe number of the comparators 22 which are "ON". For example, when alloutputs of the comparators 22 are "ON", the output of the A/D converter16 becomes X"FF" (i.e., white reference level). On the other hand, whenall the outputs of the comparators 22 are "OFF", the output of the A/Dconverter 16 becomes X"00" (i.e., black reference level). That is, forexample, when the outputs from the first to the i-th (80-th) of thecomparators 22 are "ON", the output of the A/D converter 16 becomesX"50".

As explained above, the present invention aims to eliminate thedifference of the image output between the first output by the FB typeand second output by the ADF type. In order to realize the above, thereare four correction methods in the second aspect of the presentinvention, i.e., correction by means of the white reference level,correction by means of the CCD output, correction by means of an amountof the light by the lamp, and correction by means of the conversionformula calculated by the microprocessor.

These correction methods will be explained in detail with reference tothe drawings.

Correction by means of the white reference level

FIG. 19 is an explanatory view for explaining correction by means of thewhite reference level between the FB type and the ADF type. In thedrawing, the chain dotted line denotes the white reference level, andthe dotted line denotes the white reference level after correction.Further, the left side denotes the image output by the FB type, and thelight side denotes the image output by the ADF type. The correction bymeans of the white reference level is performed as follows.

(1) The image read unit (4) reads the white reference portion (3a), andthe read data is adjusted to X"FF" by controlling the D/A converter (18)which is controlled by the microprocessor (21). Similarly, the read datais adjusted to X"00" by controlling the D/A converter (19) which iscontrolled by the microprocessor (21). Further, the microprocessor (21)controls the D/A converter (13) in order to adjust the gain of the AGCamplifier (12) so that the CCD output is included within the input rangeof the A/D converter (16).

(2) The image read unit (4) of the FB type reads the referencemanuscript having a uniform reflectance ratio. The output level of theA/D converter (16) at the i-th bit is set to a level A. The level A isstored in the work RAM in accordance with the control by themicroprocessor (21).

(3) The image read unit (4) of the ADF type reads the same referencemanuscript. The output level of the A/D converter (16) at the i'-th bit(i=i') is set to a level B. The level B is stored in the work RAM inaccordance with the control by the microprocessor (21).

(4) During read operation by the ADF type, movement of the manuscript istemporarily stopped in the vicinity of the center of the manuscript, themicroprocessor (21) compares the level A with the level B and adjuststhe white reference level of the D/A converter (18) until the level B isequal to the level A.

(5) The change rate of the white reference level is stored in the E²PROM (23) when the level B is equal to the level A under the control ofthe microprocessor (21).

(6) In the read operation by the ADF type after the above processes, thewhite reference level is stored in the white level memory (17), and thewhite reference level is corrected in accordance with the change ratestored in the E² PROM (23) by setting the change rate to the D/Aconverter (18) which is controlled by the microprocessor (21).

Correction by means of the CCD output

FIG. 20 is an explanatory view for explaining the correction of the CCDoutput between the FB type and the ADF type. In the drawing, the chaindotted line represents the white reference level, and the dotted linerepresents the CCD output level after correction. The correction bymeans of the CCD output is performed as follows.

(1) The image read unit (4) reads the white reference portion (3a), andthe read data is adjusted to X"FF" by controlling the D/A converter (18)which is controlled by the microprocessor (21). Similarly, the read datais adjusted to X"00" by controlling the D/A converter (19) which iscontrolled by the microprocessor (21). Further, the microprocessor (21)controls the D/A converter (13) in order to adjust the gain of the AGCamplifier (12) so that the CCD output is included within the input rangeof the A/D converter (16).

(2) The image read unit (4) of the FB type reads the referencemanuscript having a uniform reflectance ratio. The output level of theA/D converter (16) at the i-th bit is set to a level A. The level A isstored in the work RAM in accordance with the control by themicroprocessor (21).

(3) The image read unit (4) of the ADF type reads the same referencemanuscript. The output level of the A/D converter 16 at the i'-th bit(i=i') is set to the level B. The level B is stored in the work RAM inaccordance with the control by the microprocessor (21).

(4) During read operation by the ADF type, movement of the manuscript istemporarily stopped in the vicinity of the center of the manuscript, themicroprocessor (21) compares the level A with the level B and adjuststhe gain of the D/A converter (13) until the level B is equal to thelevel A.

(5) The change rate of the gain is stored in the E² PROM (23) when thelevel B is equal to the level A under the control by the microprocessor(21).

(6) In the read operation by the ADF type after the above processes, thewhite reference level is stored in the white level memory (17), and thegain is corrected in accordance with the change rate of the gain storedin the E² PROM (23) by setting the change rate to the D/A converter (13)which is controlled by the microprocessor (21).

Correction by means of the amount of light produced by the lamp

This correction is performed by adjusting the amount of the lightproduced by the lamp by controlling the D/A converter (11) and thetransistor unit (15) under the control of the microprocessor (21). Thecorrection by means of the amount of the light is performed as follows.

(1) The image read unit (4) reads the white reference portion (3a), andthe read data is adjusted to X"FF" by controlling the D/A converter (18)which is controlled by the microprocessor (21). Similarly, the read datais adjusted to X"00" by controlling the D/A converter (19) which iscontrolled by the microprocessor (21). Further, the microprocessor (21)controls the D/A converter (13) in order to adjust the gain of the AGCamplifier (12) so that the CCD output is included within the input rangeof the A/D converter (16).

(2) The image read unit (4) of the FB type reads the referencemanuscript having uniform reflectance ratio. The output level of the A/Dconverter (16) at the i-th bit is set to a level A. The level A isstored in the work RAM in accordance with the control by themicroprocessor (21).

(3) The image read unit (4) of the ADF type reads the same referencemanuscript. The output level of the A/D,converter 16 at the i'-th bit(i=i') is set to the level B. The level B is stored in the work RAM inaccordance with the control by the microprocessor (21).

(4) During read operation by the ADF type, movement of the manuscript istemporarily stopped in the vicinity of the center of the manuscript, themicroprocessor (21) compares the level A with the level B and adjuststhe amount of the light by controlling the transistor unit (15) and theD/A converter (11) under the control of the microprocessor (21) untilthe level B is equal to the level A.

(5) The change rate of the gain is stored in the E² PROM (23) when thelevel B is equal to the level A under the control of the microprocessor(21).

(6) In the read operation by the ADF type after the above processes, thewhite reference level is stored in the white level memory (17), and theamount of the light is corrected in accordance with the change ratestored in the E² PROM (23) by setting the change rate to the transistorunit (15) and the D/A converter (11) under the control of themicroprocessor (21).

Correction by means of the conversion formula

The output of the A/D converter (16) is sent to the microprocessor (21),and the image output is corrected by using the change rate which isobtained by the correction of the white reference level or thecorrection of the CCD output.

For example, when the white reference level is "100" and the blackreference level of the A/D converter (16) is "0", it is assumed that thefirst output is "50" when the manuscript is read by the FB type and thesecond output is "40" when the manuscript having the same reflectanceratio as above is read by the ADF type. In this case, in the readoperation by the ADF type, the output of the A/D converter (16) ismultiplied by 50/40 by the microprocessor, and the resultant data isdetermined as the read image output.

FIGS. 21A and 21B are flowcharts for explaining adjustment processesaccording to the present invention.

In step S1, the white reference level is given to the upper limit value(X'FF') of the input range of the A/D converter (16), and the blackreference level is given to the lower limit value (X'00') of the inputrange of the A/D converter (16) by controlling the D/A converter (18)for the white level and the D/A converter (19) for the black level underthe control by the microprocessor (21).

In step S2, the reference manuscript is put on the glass plate 3, andthe gain of the AGC amplifier 12 is adjusted so that the CCD output isincluded within the input range of the A/D converter by controlling theD/A converter (13) under the microprocessor (21).

In step S3, the image read unit 4 is moved to the white referenceposition 3a, and the output of the A/D converter (16) is stored in thewhite level memory 17 as the white reference level under the control bythe microprocessor (21).

In step S4, the image read unit 4 is moved to the black referenceposition 3b, and the output of the A/D converter (16) is stored in theblack level memory 20 as the black reference level under the control bythe microprocessor (21).

In step S5, the image read unit 4 in the FB type starts to read themanuscript.

In step S6, during the read operation by the FB type, the gradationlevels for several bits are stored in the work RAM (22) under thecontrol by the microprocessor (21) as the level A.

In step S7, the image read unit 4 in the ADF type starts to read thesame manuscript.

In step S8, during a read operation by the ADF type, movement of themanuscript is temporarily stopped in the vicinity of the center of themanuscript (point A or B) in order to avoid a read error caused byfluctuation of the paper.

In step S9, the gradation level at the point B (ADF type) is adjusted soas to become equal to the level A (FB type) by changing, (a) the whitereference level, (b) the gain of the AGC amplifier, or (c) the amount ofthe light, and by correcting (d) the calculation of the gradation usingthe conversion formula. The corrected value is stored in the memory, forexample, E² PROM.

In step S10, the manuscript is ejected from the image scanner.

The following are detailed explanations of above (a) to (d).

Regarding the above (a), during a read operation by the ADF type,movement of the manuscript is temporarily stopped at the predeterminedposition and the image output (i.e., level B) at that position is storedin the work RAM. The microprocessor compares the level B with the levelA which is obtained by the FB type. Further, the microprocessor adjuststhe white reference level by controlling the D/A converter (18) untilthe level B becomes equal to the level A.

Regarding the above (b), a during a read operation by the ADF type,movement of the manuscript is temporarily stopped at the predeterminedposition and the image output (i.e., level B) at that position is storedin the work RAM. The microprocessor compares the level B with the levelA which is obtained by the FB type. Further, the microprocessor adjuststhe gain of the AGC amplifier (12) by controlling the D/A converter (13)until the level B becomes equal to the level A.

Regarding the above (c), during a read operation by the ADF type,movement of the manuscript is temporarily stopped at the predeterminedposition and the image output (i.e., level B) at that position is storedin the work RAM. The microprocessor compares the level B with the, levelA which is obtained by the FB type. Further, the microprocessor adjuststhe amount of the light of the lamp by controlling the D/A converter(11) and the transistor unit (15) until the level B becomes equal to thelevel A.

Regarding the above (d), during read operation by the ADF type, movementof the manuscript is temporarily stopped at the predetermined positionand the image output (i.e., level B) at that position is stored in thework RAM. The microprocessor compares the level B with the level A whichis obtained by the FB type. Further, the microprocessor calculates thecorrection value "C" so that the level B becomes equal to the level A.That is, correction value C can be expressed by B=C×A. Where, "B" and"A" are levels as mentioned above.

We claim:
 1. An image scanner having a flat bed (FB) type structure andan automatic document feeding (ADF) type structure, comprising:a whitereference portion provided for a glass plate which holds a manuscript; ablack reference portion provided adjacent to said white referenceportion; a lamp unit for irradiating light to said manuscript; a mirrorfor reflecting the light irradiated from said lamp to said manuscript;CCD sensors for converting images on said manuscript to electricsignals; said lamp unit, said mirror and said CCD sensors forming animage read unit being used commonly in the FB type and the ADF type; anAGC amplifier connected to said CCD sensors for amplifying an output ofsaid CCD sensors and controlling the gain thereof; a microprocessor; aD/A converter for adjusting the gain of said AGC amplifier in accordancewith control by said microprocessor; a sample-hold means for samplingthe output of said AGC amplifier; a white level memory for storing awhite reference level which is obtained by reading said white referenceportion; a white level D/A converter for converting an analog whitereference level signal, which is read from said white level memory, to adigital signal; a black level memory for storing a black reference levelwhich is obtained by reading said black reference portion; a black levelD/A converter for converting the analog black reference level signal,which is read from said black level memory, to the digital signal; anA/D converter having an input terminal for receiving the analog signalfrom said sample-hold means, a white reference terminal for receivingthe output from the D/A converter, and a black reference terminal forreceiving the output from the D/A converter, and outputting the digitalsignal; a work RAM for storing various working data; and an E² PROM forstoring resultant data; wherein correction of the difference of an imageoutput between the FB type and the ADF type is performed in accordancewith a change rate of the white reference level between the FB type andthe ADF type.
 2. A correction method of difference of an image output inan image scanner having a flat bed (FB) type structure and an automaticdocument feeding (ADF) type structure, comprising:a white referenceportion provided for a glass plate which holds a manuscript; a blackreference portion provided adjacent to said white reference portion; alamp unit for irradiating light to said manuscript; a mirror forreflecting the light irradiated from said lamp to said manuscript; CCDsensors for converting images on said manuscript to electric signals;said lamp unit, said mirror and said CCD sensors forming an image readunit being used commonly in the FB type and the ADF type; an AGCamplifier connected to said CCD sensors for amplifying an output of saidCCD sensors and controlling the gain thereof; a microprocessor; a D/Aconverter for adjusting the gain of said AGC amplifier in accordancewith control by said microprocessor; a sample-hold means for samplingthe output of said AGC amplifier; a white level memory for storing awhite reference level which is obtained by reading said white referenceportion; a white level D/A converter for converting an analog whitereference level signal, which is read from said white level memory, to adigital signal; a black level memory for storing a black reference levelwhich is obtained by reading said black reference portion; a black levelD/A converter for converting the analog black reference level signal,which is read from said black level memory, to the digital signal; anA/D converter having an input terminal for receiving the analog signalfrom said sample-hold means, a white reference terminal for receivingthe output from the D/A converter, and a black reference terminal forreceiving the output from the D/A converter, and outputting the digitalsignal; a work RAM for storing various working data; and an E² PROM forstoring resultant data; wherein correction of the difference of an imageoutput between the FB type and the ADF type is performed in such amanner that;first, said image read unit of the FB type reads a referencemanuscript having a uniform reflectance ratio, and a first output ofsaid A/D converter is stored in said work RAM; next, said image readunit of the ADF type reads the same reference manuscript and outputs asecond output from said A/D converter, further, a level of the whitereference level signal at the white reference terminal of said A/Dconverter is adjusted by controlling said D/A converter for the AGCwhich is controlled by the microprocessor so that the second outputbecomes equal to the first output, and a change rate of the whitereference level signal is stored in said E² PROM when the first outputis equal to the second output; and finally, when said image read unitreads said manuscript by using the ADF type, the output from said whitelevel D/A converter is changed in accordance with the change rate whichis stored in said E² PROM.
 3. A method as claimed in claim 2, whereinsaid correction of the difference of the image output between the FBtype and the ADF type is performed in such a manner that;first, saidimage read unit of said FB type reads the reference manuscript having auniform reflectance ratio, and the first output of said A/D converter isstored in said work RAM; next, said image read unit of the ADF typereads the same reference manuscript and outputs the second output fromsaid A/D converter, further, the gain of said amplifier and sample-holdmeans is adjusted by controlling said D/A converter for the AGC which iscontrolled by said microprocessor so that the second output becomesequal to the first output, and the change rate of the gain is stored insaid E² PROM when the first output is equal to the second output; andfinally, when said image read unit reads said manuscript by using theADF type, the gain of said amplifier and sample-hold means is changed inaccordance with the change rate which is stored in said E² PROM.
 4. Amethod as claimed in claim 2, wherein said correction of the differenceof the image output between the FB type and the ADF type is performed insuch a manner that;first, said image read unit of the FB type reads thereference manuscript having a uniform reflectance ratio, and the firstoutput of the A/D converter is stored in said work RAM; next, said imageread unit of the ADF type reads the same reference manuscript andoutputs the second output from said A/D converter, further, the tubecurrent of said lamp is adjusted by controlling a D/A converter for tubecurrent which is controlled by said microprocessor so that the secondoutput becomes equal to the first output, and the change rate of thetube current is stored in said E² PROM when the first output is equal tothe second output; and finally, when said image read unit reads saidmanuscript by using the ADF type, the tube current of the lamp ischanged in accordance with the change rate which is stored in said E²PROM.
 5. A method as claimed in claim 2, wherein said correction of thedifference of the image output between the FB type and the ADF type isperformed in such manner that;first, said image read unit of the FB typereads the reference manuscript having uniform reflectance ratio, and thefirst output of said A/D converter is stored in said work RAM; next,said image read unit of the ADF type reads the same reference manuscriptand outputs the second output from said A/D converter, further, inaccordance with the first and second outputs, a conversion formula isgenerated so that the first output becomes equal to the second output,and the resultant formula is stored in said E² PROM; and finally, whensaid image read unit reads said manuscript by using the ADF type, theoutput of the A/D converter is changed in accordance with the resultantformula which is stored in said E² PROM by using the microprocessor. 6.An image scanner having a flat bed (FB) type structure and an automaticdocument feeding (ADF) type structure, said image scanner comprising:awhite reference portion provided for a glass plate which holds amanuscript; a black reference portion provided adjacent to said whitereference portion; a lamp unit for irradiating light to said manuscript;CCD sensors for converting images on said manuscript to electricsignals; said lamp unit, said CCD sensors forming an image read unitbeing used commonly in the FB type and the ADF type; an AGC amplifierconnected to said CCD sensors for amplifying an output of said CCDsensors and controlling the gain thereof; a microprocessor; a D/Aconverter for adjusting the gain of said AGC amplifier in accordancewith control by said microprocessor; a sample-hold means for samplingthe output of said AGC amplifier; a white level memory for storing awhite reference level which is obtained by reading said white referenceportion; a white level D/A converter for converting an analog whitereference level signal, which is read from said white level memory, to adigital signal; a black level memory for storing a black reference levelwhich is obtained by reading said black reference portion; a black levelD/A converter for converting the analog black reference level signal,which is read from said black level memory, to the digital signal; anA/D converter having an input terminal for receiving the analog signalfrom said sample-hold means, a white reference terminal for receivingthe output from the D/A converter, and a black reference terminal forreceiving the output from the D/A converter, and outputting the digitalsignal; a memory for storing resultant data; wherein correction of thedifference of an image output between the FB type and the ADF type isperformed in accordance with a change rate of the white reference levelbetween the FB type and the ADF type.
 7. A correction method ofdifference of an image output in an image scanner having a flat bed (FB)type structure and an automatic document feeding (ADF) type structure,comprising:a white reference portion provided for a glass plate whichholds a manuscript; a black reference portion provided adjacent to saidwhite reference portion; a lamp unit for irradiating light to saidmanuscript; CCD sensors for converting images on said manuscript toelectric signals; said lamp unit and said CCD sensors forming an imageread unit being used commonly in the FB type and the ADF type; an AGCamplifier connected to said CCD sensors for amplifying an output of saidCCD sensors and controlling the gain thereof; a microprocessor; a D/Aconverter for adjusting the gain of said AGC amplifier in accordancewith control by said microprocessor; a sample-hold means for samplingthe output of said AGC amplifier; a white level memory for storing awhite reference level which is obtained by reading said white referenceportion; a white level D/A converter for converting an analog whitereference level signal, which is read from said white level memory, to adigital signal; a black level memory for storing a black reference levelwhich is obtained by reading said black reference portion; a black levelD/A converter for converting the analog black reference level signal,which is read from said black level memory, to the digital signal; anA/D converter having an input terminal for receiving the analog signalfrom said sample-hold means, a white reference terminal for receivingthe output from the D/A converter, and a black reference terminal forreceiving the output from the D/A converter, and outputting the digitalsignal; a memory for storing resultant data; wherein correction of thedifference of an image output between the FB type and the ADF type isperformed in such a manner that;first, said image read unit of the FBtype reads a reference manuscript having a uniform reflectance ratio,and a first output of said A/D converter is stored in a work memory;next, said image read unit of the ADF type reads the same referencemanuscript and outputs a second output from said A/D converter, further,a level of the white reference level signal at the white referenceterminal of said A/D converter is adjusted by controlling said D/Aconverter for the AGC which is controlled by the microprocessor so thatthe second output becomes equal to the first output, and a change rateof the white reference level signal is stored in said memory when thefirst output is equal to the second output; and finally, when said imageread unit reads said manuscript by using the ADF type, the output fromsaid white level D/A converter is changed in accordance with the changerate which is stored in said memory.